The invention relates to an air-driven low-frequency sound generator provided with a system for positive feedback.
A low-frequency sound generator with a positive feedback system is described in EP, A, No. 0 006 833, comprising, as a sound emitter, an open resonator for generating standing gas-borne sound waves which produce a varying gas pressure in the resonator; and a feeder having a pipe for the supply of pressure gas to the resonator and a movable resilient valve slide whose position remains unaffected by the pressure gas and which regulates the gas flow from the pipe while creating a modulated flow of pressure gas to the resonator. Thus the valve slide is connected to a sound-actuated diaphragm mounted inside the resonator. The valve slide is a sleeve-type slide which is axially and displaceably guided inside or outside of the pipe. The pipe is connected to a pressure gas source and the purpose of the valve slide is to control an opening in the pipe-wall for the supply of pressure gas.
The basic principle for the operation of the above described low-frequency generator is: when the sound pressure inside the resonator is higher than the surrounding atmospheric pressure, the valve slide will move in such a direction to free the opening and air having a higher pressure than the sound pressure will then be fed into the resonator. Accordingly, when the sound pressure inside the resonator is lower than the surrounding atmospheric pressure, the valve slide will be forced to move in the opposite direction with the result that the opening is closed.